Control device for internal combustion engine and a continuously variable transmission

ABSTRACT

A control device for an internal combustion engine and a continuously variable transmission of a vehicle according to the present invention comprises the continuously variable transmission disposed between the internal combustion engine and driving wheels and enables controlling the output of the internal combustion engine. In particular, objective driving torque Tet is set according to driving torque Td applied to a vehicle, driving torque correcting amount T IV  which serves as a first running resistance of the vehicle according to vehicle acceleration, transmission torque fluctuation correcting amount Tcv which serves as a second running resistance due to being consumed in the transmission operation mode of the continuously variable transmission, and vehicle body correcting torque Tv, which is necessary for eliminating a deviation Δv between an objective vehicle speed Vt and an actual vehicle speed Vc, required for eliminating this deviation Δv to control the output of the internal combustion engine with this objective driving torque. Accordingly, the internal combustion engine can be controlled with the output corresponding to a value of the objective driving torque Tet set by selectively using an optimum torque correcting amount depending on driving conditions. This results in elimination of slip of a transmission steel belt caused by excessive output and shock in the transmission operation.

TECHNICAL FIELD

This invention relates to a control device for an internal combustionengine and a continuously variable transmission. The control device isconnected to the continuously variable transmission disposed between theinternal combustion engine and driving wheels, and changes and controlsa transmission ratio of the continuously variable transmission at atransmission ratio changing speed suitable for driving conditions of thevehicle while controlling an output of the internal combustion engine.

DESCRIPTION OF RELATED ART

Generally, engine output (hereinafter, referred merely as "output") ofan internal combustion engine (hereinafter, referred merely as anengine) mounted on a vehicle is mechanically controlled by a throttledevice coupled to a driver-operable member such as an accelerator pedaland a throttle lever (which are representatively referred as acceleratorpedal hereinafter) through an accelerator cable.

The accelerator pedal and the throttle device cooperate with each othersuch that the displacement corresponding to a stepping amount of theaccelerator pedal is transmitted to the throttle device and a throttlevalve in the device is actuated at this displacement (stepping amount).Unfortunately, excessive output may be generated due to careless drivingand lack of skill of a driver. Consequently a vehicle may slide onstarting, slip on the icy ground, and skid (slip) at a suddenacceleration.

Accordingly, methods have been proposed such as a dual throttle valvemethod where a main throttle valve and a sub-throttle valve are arrangedin the throttle device. The sub-throttle valve is electronicallycontrolled and a traction control (power control) method utilizing theso called drive-by-wire method is used. In this method, the acceleratorcable is not disposed between the accelerator pedal and the throttlevalve, and an opening of the accelerator pedal is detected by using asensor such as a potentiometer. The throttle valve is then operated by astepping motor or the like based on output of the sensor.

In the traction control method of the type described, an ECU (enginecontrol unit) generally calculates an optimum opening (i.e., targetengine output) for the sub-throttle valve and the main throttle valve inaccordance with the data (1) representative of the rotation condition ofthe front and rear wheels and (2) a step amount for the acceleratorpedal. The ECU controls a driving torque of the wheels in a range not tocause the undesirable skid.

Information regarding the required output of the engine is properly setin accordance with, for example, the opening of the accelerator pedal.As mentioned above, the ECU calculates and sets the required output ofthe engine when using the traction control method for drivinglycontrolling the sub-throttle valve and the main throttle valve so as toobtain the required output. In this event, it is preferable to carry outthe calculation of the required output with respect to an actual torqueunder current engine conditions. More specifically, by calculating adeviation between a required torque and the actual torque and bycarrying out a real-time control to eliminate the deviation, it ispossible to prevent an over-control and poor response of the controldevice.

While the actual torque of the engine can be detected by a bench testusing a chassis dynamometer, it is difficult in practice to mount it ona vehicle due to the weight, size, and costs of the device. Plus thereis a serious defect that output (energy) loss is inevitably caused.

Accordingly, it is assumed that precision of the output control can beimproved by calculating the actual torque in accordance with intake airflow information by using a conventional control system.

One power transmission method for transmitting output torque of theengine to wheels is variable transmission. As one such transmission, acontinuously variable transmission (CVT) can continuously change thetransmission ratio by using a steel belt and pulleys, and can increaseor decrease a transmission ratio changing speed depending on a hydraulicvalue supplied to an hydraulic actuator.

In the continuously variable transmission of the type described, thetransmission ratio changing speed, is calculated so as to eliminate atransmission ratio deviation between an objective transmission ratiowhich is calculated in accordance with the driving conditions and anactual transmission ratio. The hydraulic actuator of the continuouslyvariable transmission is controlled in order to obtain the transmissionratio changing speed.

Problems to be solved by the present invention are as follows.

When the continuously variable transmission CVT and a cruise controlsystem are mounted on a conventional vehicle, the following problems arecaused. That is, when the transmission ratio of the continuouslyvariable transmission CVT is changed at a relatively low speed, thetorque on the drive shaft is smoothly changed. On the other hand, when adeviation between the target transmission ratio and the actualtransmission ratio is relatively large, the transmission ratio has to bechanged rapidly and extensively. However, the continuously variabletransmission CVT consumes operational torque, and the moment of inertiaof pulleys is relatively large, which adversely affects acceleration ofthe vehicle, causing undesired excessive shock during the transmissionoperation. In addition, excessive torque of the engine may result inslide of a steel belt. Accordingly, it is disadvantageous in that thevehicle speed may be varied on applying (engine brake at a downhill roador on operating the cruise control due to shocks during the transmissionoperation of the continuously variable transmission CVT even when theengine output is constant and the load is constant.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a control device for aninternal combustion engine and a continuously variable transmissionwhich can control a preset vehicle speed without any fluctuation thereofwhen the transmission ratio of the continuously variable transmission ischanged.

According to the present invention for controlling both an internalcombustion engine and a continuously variable transmission, the controldevice for an internal combustion engine and a continuously variabletransmission comprises: driving torque detecting means for detectingdriving torque applied to a vehicle; acceleration detecting means fordetecting actual acceleration of the vehicle; driving torque correctingamount setting means for setting a driving torque correcting amount as afirst running resistance of the vehicle in accordance with theacceleration detected by the acceleration detecting means; transmissionspeed ratio changing speed detecting means for detecting transmissionratio changing speed which is a changing rate of the transmission ratioof the continuously variable transmission; transmission torquefluctuation correcting amount setting means for setting a transmissiontorque fluctuation correcting amount which corresponds to torque (i.e. asecond running resistance) consumed for the transmission operation ofthe continuously variable transmission in accordance with thetransmission ratio changing speed detected by the transmission ratiochanging speed detecting means; vehicle speed detecting means fordetecting an actual vehicle speed of the vehicle; a vehicle speedcorrecting torque setting means for setting vehicle speed correctingtorque, which is necessary for eliminating a deviation between anobjective vehicle speed and the actual vehicle speed detected by saidvehicle speed detecting means; objective driving torque setting meansfor setting objective driving torque in accordance with the drivingtorque detected by the driving torque detecting means, the drivingtorque correcting amount set by the driving torque correcting amountsetting means, the transmission torque fluctuation correcting amount setthe transmission torque fluctuation correcting amount setting means, andthe vehicle speed correcting torque set by the vehicle speed correctingtorque setting means; and output controlling means for controllingoutput of the internal combustion engine in accordance with theobjective driving torque set by the objective driving torque settingmeans.

Thus, the objective driving torque is set in accordance with the drivingtorque, the driving torque correcting amount, the transmission torquefluctuation correcting amount, and the vehicle speed correcting torque.In addition, the output of the internal combustion engine may becontrolled by means of the objective driving torque. Accordingly, theobjective driving torque can be set in consideration with the optimumtorque correcting amount depending on the driving conditions. It ispossible to control the internal combustion engine at optimum output forthe value. Further, it is possible to eliminate slip of the steel beltcaused by excessive output and shocks during the transmission operationand, in turn, to improve driving feelings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a whole structural diagram of a control device for an internalcombustion engine and a continuously variable transmission according toone embodiment of the present invention;

FIG. 2 is a functional block diagram of an electronic control deviceapplied to the device illustrated in FIG. 1 of the present invention;

FIG. 3 is a sectional view of a continuously variable transmissionapplied to the device illustrated in FIG. 1;

FIG. 4 shows a characteristic curve of a transmission ratiocorresponding engine speed calculating map for use in output controlcarried out by the device illustrated in FIG. 1;

FIG. 5 shows a characteristic curve of an intake air flow/torquecalculating map for use in output control carried out by the deviceillustrated in FIG. 1;

FIG. 6 shows a characteristic curve of a throttle valve (accelerator)opening/intake air flow calculating map for use in the output controlcarried out by the device illustrated in FIG. 1;

FIG. 7 is a flow chart representing an engine output control processingroutine carried out by the device illustrated in FIG. 1;

FIG. 8 is continuation of FIG. 7;

FIG. 9 is a flow chart of a running resistance estimating routinecarried out by the device illustrated in FIG. 1;

FIG. 10 is a flow chart of a CVT control routine carried out by thedevice illustrated in FIG. 1;

FIG. 11 is a flow chart of a main routine carried out by the controldevice illustrated in FIG. 1;

FIG. 12 shows a characteristic curve of a dowel angle calculating mapfor use in output control carried out by the control device illustratedin FIG. 1;

FIG. 13 is a characteristic curve of an i/transmission speed calculatingmap for use in the output control carried out by the control deviceillustrated in FIG. 1;

FIG. 14(a) is a schematic view of a part of an operational modelrepresenting a pulley portion in the CVT of the device illustrated inFIG. 1;

FIG. 14(b) shows a characteristic curve of a hydraulicpressure/transmission ratio changing speed calculating map for thedevice illustrated in FIG. 1; and

FIG. 15 is a schematic view of a dynamic model of the CVT illustrated inFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a schematic diagram of a gasoline engine system(hereinafter, referred simply as an engine system) and a powertransmission system P, which utilizes a control device according to thepresent invention. FIG. 2 shows a block diagram of the control deviceinternal combustion engine and a continuously variable transmissionaccording to the present invention.

The present invention basically controls both the engine E mounted on avehicle and the continuously variable transmission (CVT) 35 which isdisposed in the power transmission system P between the engine E anddriving wheels 32 and of which transmission ratio i can be continuouslychanged. Particularly, the present invention comprises: driving torquedetecting means A1 for detecting driving torque Td applied to thevehicle; acceleration detecting means A2 for detecting actualacceleration (dv/dt) of the vehicle; driving torque correcting amountsetting means A3 for setting a driving torque correcting amount T_(IV)as a first running resistance of the vehicle in accordance with theacceleration (dv/dt); transmission ratio changing speed detecting meansA4 for detecting transmission ratio changing speed which is a changingrate of the transmission ratio i for the continuously variabletransmission 35; transmission torque fluctuation correcting amountsetting means A5 for setting a transmission torque fluctuationcorrecting amount Tcv which corresponds to torque (i.e. a second runningresistance) for the transmission operation of the continuously variabletransmission 35 in accordance with the transmission ratio changing speeddetected by the transmission ratio changing speed detecting means A4;vehicle speed detecting means A6 for detecting an actual vehicle speedvc; vehicle speed correcting torque setting means A7 for setting vehiclespeed correcting torque Tv, which is necessary for eliminating adeviation Δv, between an objective vehicle speed vt for allowing thevehicle to be traveled at a constant speed and the actual vehicle speedvc detected by the vehicle speed detecting means; objective drivingtorque setting means A8 for setting objective driving torque Tet inaccordance with the driving torque Td, the driving torque correctingamount T_(IV), the transmission torque fluctuation correcting amountTcv, and the vehicle speed correcting torque Tv; and output controllingmeans A9 for controlling output of the internal combustion engine inaccordance with the objective driving torque Tet.

Thus, the objective driving torque Tet is set in accordance with thedriving torque Td, the driving torque correcting amount T_(IV), thetransmission torque fluctuation correcting amount Tcv, and the vehiclespeed correcting torque Tv. Thus, the output of the internal combustionengine can be controlled by means of the objective driving torque Tet.Accordingly, the objective driving torque Tet can be set by selectivelyapplying the torque correcting amount depending on the drivingconditions. Further, it is possible to control the internal combustionengine at the optimum output in accordance with the objective drivingtorque Tet. It is also possible to eliminate slip of the steel beltcaused by excessive output and shock caused during the transmissionoperation and, thereby improving driving feelings.

Now, a whole structure of the engine system and the power transmissionsystem P illustrated in FIG. 1 will be described below. The enginesystem comprises an electronically controlled injection four-cycleengine E and variable devices such as fuel injectors 1 by which fuel issprayed and injected and spark plugs 2 for ignition are controlled by aDBWECU 3 which acts as electronic control means for the engine. Inaddition, the DBWECU 3 is connected to a CVTECU 21 which acts as theelectronic control means for the continuously variable transmission(CVT) 35, and to a cruise control circuit 39. The cruise control circuit39 comprises a constant speed switch and a release switch (not shown)arranged in front of a driver's seat (not shown). The cruise controlcircuit 39 can supply a constant speed command or release command and tothe DBWECU 3 in response to the operation of these switches. Both ECUs 3and 21 are connected with each other through a communication line tocontinuously send and receive signals therebetween.

The DBWECU 3 is connected to an actuator 11 for actuating a throttlevalve 9 which serves as intake air flow adjusting means which is drivenwithout being affected by the operation of an accelerator pedal 10 whichserves as a driver-operable member. The CVTECU 21 is connected to ahydraulic actuator 23 for hydraulically controlling the transmissionratio changing speed of the continuously variable transmission 35.

An entire construction of the engine system will be described belowalong a direction in which the air flows.

An intake air taken through an air cleaner element 5 is subjected to anair flow sensor 6 of the Karman vortex type which acts as intake airflow detecting means to detect the air flow and is delivered to athrottle body 8 through a suction pipe 42. Inside of an air cleaner body4, apparatus such as an atmospheric pressure sensor and an atmospherictemperature sensor are not shown disposed besides the air flow sensor 6to determine data on the intake air such as an atmospheric pressure apand an atmospheric temperature at, supplied to the DBWECU 3 in awell-known manner.

The intake air flow into the throttle body 8 is controlled by means ofthe throttle valve in a butterfly shape. The throttle valve 9 is notactuated by the accelerator pedal 10 stepped by the driver. It isactuated by the actuator 11 (in this embodiment, a stepping motor). Inthis embodiment, so called DBW (drive by wire) method is applied wherethe actuator 11 is controlled by the DBWECU 3. In FIG. 1, a referencenumeral 12 represents a throttle position sensor (hereinafter, athrottle sensor) for supplying opening information relating to thethrottle valve 9, and a detection signal thereof is supplied to theDBWECU 3.

The accelerator pedal 10 is connected to an accelerator opening sensor13 of a potentiometer type which acts as acceleration requirementdetecting means. The stepping amount θa of the accelerator pedal 10 issupplied to the DBWECU 3 after being converted to an electric signal asacceleration requirement information for a driver.

The intake air flowing into the throttle body 8 is delivered through asurge tank 14 to an intake manifold 15. The intake air flows to thedownstream of the intake manifold 15, where the fuel is injected fromthe injector 1 controlled by the DBWECU 3. Thus, the intake air and thefuel become an air fuel mixture. The air fuel mixture is poured into acombustion chamber E3 by opening a suction valve E2 disposed in theengine E. The air fuel mixture is then ignited by using the spark plug 2at or around a top dead center. After completion of theexplosion/expansion stroke, the air fuel mixture is supplied into anexhaust manifold 16 of an exhaust path 20 as exhaust gas by opening anexhaust valve E4, and is sent through an exhaust gas purification systemwhich is not shown. After the removal of toxic components, the exhaustgas is then discharged to the outside through a muffler (not shown).Reference numeral 24 represents an engine speed sensor for supplyingengine speed information, reference numeral 43 represents a linear airfuel ratio sensor which provides air fuel ratio information on all airfuel ratio zones, reference numeral 44 represents a crank angle sensorfor supplying engine crank angle information, reference numeral 45represents a knocking sensor for supplying knocking information of theengine, and reference numeral 46 represents a water temperature sensor.

On the other hand, the engine E is connected to the power transmissionsystem P and also E is connected via a crankshaft, to the continuouslyvariable transmission 35 illustrated in FIG. 3. An output shaft of anelectromagnetic clutch 25 is coupled to a primary shaft 22 of thecontinuously variable transmission 35. The primary shaft 22 is unitedwith a pair of primary pulleys stationary and movable pulleys 26 where asteel belt 27 passes through. The steel belt 27 passes between theprimary pulleys 26 and a pair of secondary pulleys 28 (stationary andmoveable pulleys). The secondary pulleys 28 are united with a secondaryshaft 29. The secondary shaft 29 is constructed such that the turningeffort is transmitted to driving wheels 32,32, which are coupled to adriving shaft 31, via a reduction gear train 30 and a differential gearwhich is not shown.

One of the primary pulleys 26 (i.e. movable pulley) serves as a part ofa piston unit of a hydraulic actuator 36. A primary pressure istransmitted to the actuator 36 through a first solenoid valve 33 from ahydraulic source 37. Similarly, one of a pair of the secondary pulleys28 serves as a part of a piston unit of a hydraulic actuator 38. A linepressure is transmitted through a second solenoid valve 34 to thehydraulic source 37.

Therefore, the effective diameter of each pulley can be relativelychanged according to the opening/closing ratio (duty ratio) of the firstand the second solenoid valves 33 and 34, respectively. In this manner,the transmission ratio can be changed by means of changing engagementwith the steel belt 27 to the pulleys.

Both solenoid valves 33 and 34 are constructed in such a manner thatthey can be operatively controlled in response to an output of theCVTECU 21. Reference numeral 40 represents a transmission ratiodetecting sensor for supplying transmission ratio information of thecontinuously variable transmission 35. The transmission ratio detectingsensor 40 comprises a pair of rotary sensors 401 and 402 for detectingrotation speeds Wcf and Wcr of the primary pulleys 26 and the secondarypulleys 28, respectively, and an arithmetic unit 403 which calculates anactual transmission ratio in (=Wcf/Wcr). The output Wcr of the rotarysensor 402 of the secondary pulleys 28 is multiplied by a predeterminedtransmission ratio α to calculate an output shaft rotational speed ωc,which serves as a vehicle speed sensor 48.

Now, each of the DBWECU 3 and the CVTECU 21, which acts as theelectronic control means, is mainly implemented by a microcomputer. Amemory circuit constituted therein memorizes and processes each controlprogram such as the transmission ratio corresponding engine speedcalculating map illustrated in FIG. 4, the torque calculating mapillustrated in FIGS. 5 and 6, the engine output control processingroutine illustrated in FIGS. 7 and 8, the running resistance estimatingroutine illustrated in FIG. 9, the CVT control processing routineillustrated in FIG. 10, and the main routine of the DBWECU 3 illustratedin FIG. 11.

The DBWECU 3 and the CVTECU 21 comprise: the driving torque detectingmeans A1 for detecting driving torque Td applied to the vehicle inaccordance with the intake air flow A/N of the internal combustionengine and the transmission ratio i of the continuously variabletransmission; acceleration detecting means A2 for detecting actualacceleration (dv/dt) of the vehicle; driving torque correcting amountsetting means A3 for setting a driving torque correcting amount T_(IV)as a first running resistance of the vehicle in accordance with theacceleration (dv/dt); transmission ratio changing speed detecting meansA4 for detecting transmission ratio changing speed which is a changingrate of the transmission ratio i of the continuously variabletransmission 35; transmission torque fluctuation correcting amountsetting means A5 for setting a transmission torque fluctuationcorrecting amount Tcv as a second running resistance which is consumedfor the transmission operation of the continuously variable transmission35 in accordance with the transmission ratio changing speed (di/dt), andsetting Tcv to zero when the continuous variable transmission is not inthe transmission operation; vehicle speed detecting means A6 fordetecting actual vehicle speed vc; vehicle speed correcting torquesetting means A7 for setting vehicle speed correcting torque Tv, whichis necessary for eliminating the deviation Δv between an objectivevehicle speed vt for allowing the vehicle to be traveled at constantspeed and the actual vehicle speed vc detected by the vehicle speeddetecting means; objective driving torque setting means A8 for settingobjective driving torque Tet in accordance with the driving torque Td,the driving torque correcting amount T_(IV), the transmission torquefluctuation correcting amount Tcv and the vehicle speed correctingtorque Tv when the continuously variable transmission is on transmissionand setting objective driving torque Tet in accordance with the drivingtorque Td, the driving torque correcting amount T_(IV) and the vehiclespeed correcting torque Tv substantially without using the transmissiontorque fluctuation correcting amount Tcv when the continuously variabletransmission is not in the transmission operation because thetransmission torque fluctuation correcting amount Tcv is set to zero bythe transmission torque fluctuation correcting amount setting means A5;and output controlling means A9 for controlling the output of theinternal combustion engine in accordance with the objective drivingtorque Tet.

Particularly in this embodiment, the control device further comprises:operational amount detecting means A10 for detecting an operationalamount θa of the driver-operable member for operating intake air flowadjusting means disposed in the suction system of the internalcombustion engine; objective transmission ratio setting means All forsetting an objective transmission ratio io in accordance with theoperational amount θa; transmission ratio detecting means A12 fordetecting an actual transmission ratio in (=Wcf/Wcr) by means of therotational speeds (Wcf, Wcr) of both pulleys in the continuouslyvariable transmission 35; transmission ratio deviation calculating meansA13 for calculating a deviation Δi between the objective transmissionratio io and the actual transmission ratio in; objective transmissionratio changing, speed setting means A14 for setting objectivetransmission ratio changing speed Vm in accordance with the transmissionratio deviation Δi; and transmission controlling means A15 forcontrolling the continuously variable transmission 35 to perform thetransmission operation at the objective transmission ratio changingspeed Vm.

Description will be made below regarding the control device for theinternal combustion engine and the continuously variable transmissionillustrated in FIGS. 1 and 2 in conjunction with the control programsillustrated in FIGS. 7 through 11.

In this embodiment, controls in the DBWECU 3 and the CVTECU 21illustrated in FIG. 1 are carried out in operation when the enginesystem E is driven by operating an ignition key which is not shown.

As the control is started, the DBWECU 3 carries out a main routineillustrated in FIG. 11. At the beginning of the main routine,initialization operation which is not shown is carried out at step c1 toread data detected by the sensors and store them in a predeterminedarea.

Step c2 determines whether or not fuel cut is mainly carried out in theengine on the basis of an engine speed Ne and engine load information(the intake air flow A/N in this embodiment). If the fuel-cutting is inprogress, the control passes to step c3 to clear an air fuel feedbackflag FBF. A fuel cut flag FCF is set to 1 at step c4. Thereafter, thecontrol returns to the step c1.

When the fuel-cutting is not performed, the control passes to steps c5and c6. The fuel cut flag FCF is reset, and whether or not a well-knownair fuel ratio feedback control condition is satisfied is determined.When this condition is not satisfied due to, for example, a transientdriving state such as a power driving state of the engine, an air-fuelratio correcting coefficient KMAP is calculated at step c12 depending onthe current driving conditions (A/N, Ne). This value is stored in anaddress KAF. Then, the control passes to step c9.

When step c7 is carried out because the air-fuel ratio feedback controlcondition is satisfied, a correcting value KFB is calculated inaccordance with the feedback control constant and data supplied from theair fuel ratio sensor 43.

The value KFB is stored in the address KAF and the control processproceeds to the step c9. At the step c9, a fuel injection pulse widthcorrecting coefficient KDT and a dead time correcting value TD for thefuel injection valve are set according to the driving condition. Inaddition, various correcting values are calculated so as to determine aspark timing θadv by using the following equation (1). Then, the controlpasses to step c10.

    θadv=θb+θwt+θap+θat+θret (1)

The collected values are a water temperature correcting value θwt toadvance the spark timing depending on the decrease of the watertemperature, and atmospheric pressure correcting value θap to advancethe spark timing depending on the decrease of the atmospheric pressure,and an intake air temperature correcting value θat to advance the sparktiming depending on the decrease of intake air temperature. Thesecorrecting values are stored in the predetermined area.

At step c10, a dowel angle is determined by using, for example, a mapillustrated in FIG. 12 in such a manner that it increases as the enginespeed Ne increases.

Thereafter, an engine output control processing is carried out at stepc11, and then the control returns to the step c1.

In FIG. 7, the engine output control processing carried out at the stepc11 is illustrated. Step a1 carries out initialization operation. Atstep a2, data such as the accelerator opening θa and the engine speed Neare stored in the predetermined area.

Step a3 determines whether or not a signal indicative of the cruisecontrol is supplied from the cruise control circuit 39. If no cruisecontrol is in progress, the control returns to the main routine.Otherwise, the control goes to the step a4.

In step a4, the vehicle speed vt is determined in response to vehiclespeed setting command supplied from the cruise control device, and isstored in a predetermined area. In addition, step a5 detects the actualvehicle speed vc, and step a6 calculates the vehicle speed deviation Δv(=vt-vc).

At step a7, a vehicle speed correcting torque Tv(=Kp×ΔV+Kd×(dΔV/dt)+∫KiΔVdt) is calculated by PID-processing thesuccessively calculated vehicle speed deviation Δv and is stored in apredetermined area.

At step a8, the running resistance Tr is estimated by means of therunning resistance estimating map illustrated in FIG. 9, and data suchas the vehicle speed vc is stored at step d1.

Then, step d2 calculates the acceleration of the vehicle bydifferentiating the vehicle speed vc depending on the output shaftrotation angular velocity of the continuously variable transmission 35.Subsequently, the driving torque correcting value T_(IV) (Ie×in²+Iv)×(dvt/dt)) is calculated at step d3 by the vehicle accelerationdepending on the vehicle speed vc and is stored in a predetermined area,where Ie represents moment of inertia of the engine, Iv representsmoment of inertia of the vehicle and i represents the transmissionratio.

At step d4, the engine output torque Te is calculated on the basis ofthe intake air flow A/N by using the torque calculating map illustratedin FIG. 5. The engine output torque Te is multiplied by the transmissionratio i, from which the mechanical loss Tloss varying with a watertemperature is subtracted to obtain the driving torque Td applied to thevehicle.

Step d5 checks whether or not the continuously variable transmission 35is currently changing the transmission ratio thereof. If thetransmission operation is not carried out, the control process passes tostep d7. Otherwise, the control process goes to step d6. Whether or notthe continuously variable transmission 35 is in the transmissionoperation is made by differentiating the output supplied from thearithmetic unit 403 for calculating the actual transmission ratio in(=wcf/wcr) and comparing with the threshold value din/dr.

When the differentiated value is smaller than the threshold valuedin/dr, the continuously variable transmission 35 is considered to be onthe transmission operation. Then, the transmission torque fluctuationcorrecting amount Tcv is set to zero. On the other hand, when thedifferentiated value is larger than the threshold value din/dr, thetransmission torque fluctuation correcting value Tcv (=(Ie×ωe)×di/dt) iscalculated. Here, the transmission torque fluctuation correcting amountTcv is a torque value which is considered to be consumed fortransmission operation and is calculated. The transmission ratiochanging speed di/dt is calculated by multiplying the rotation speed Wcrof the secondary pulley 28 by the predetermined transmission ratio and adifferential ratio, and by differentiating the proportion of therotation speed of the continuously variable transmission to the enginerotation speed ωe.

The transmission torque fluctuation correcting value Tcv is obtained asfollows.

In the dynamic model of the CVT as illustrated in FIG. 15, the primarypulley 26 having the moment of inertia Ie is supplied with the torque Teat an angular velocity of we from a torque converter (t). Then, thetorque Te is transmitted to the steel belt (st). The secondary pulley 28having the moment of inertia Ic2 is supplied with the torque Tv at anangular velocity of ωv from the steel belt (st), and the torque Tv istransmitted to the output side (d) of the CVT. In this way, the torqueTe is inputted, and the torque Tv is outputted through the belt (st)between both pulleys when the transmission ratio i is being changed. Thekinetic equations for the primary and secondary pulleys are:

    Ie×(dωe/dt)=Te-Te'                             (2)

    Iv×(dωv/dt)=Tv'-Tv                             (3)

In this event,

dωe/dt=d(i×ωv)/dt=(di/dt)×ωv+i×(d.omega.v/dt), and

Te'=(1/i)×Tv'

can be obtained, and the results are re-written by the equation (2),namely, ##EQU1##

The equation (2)' is multiplied by i, and added to both sides of theequation (3). Further, when the resultant equation is rearranged inconsideration of ωe=1×ΔV,

    dωv/dt=(i×Te-Tv)/(Iv+i.sup.2 ×Ie)-(Iex(di/dt)×ωe)/(Iv+i.sup.2 ×Ie) (4)

can be obtained.

As well known in the art, the transmission ratio changing speed di/dtcan be controlled by changing the hydraulic pressure P applied to thepulleys. Accordingly, the following equation is obtained,

    di/dt=f(p), imin≦i≦imax

where the torque Tv of the output shaft (d) of the CVT obtained by theequation (4) is substituted by transmission torque T_(RL) transmitted bythe transmission and torque corresponding to the loss T_(L) consumed bythe transmission, namely,

    dωe/dt(i×Te-T.sub.RL -T.sub.n)/(Ie×i.sup.2 +Iv)-((di/dt)×107 e)/(Ie×.sup.2 =Iv),

where the second term represents the torque value depending on avariation of the transmission ratio changing speed di/dt. Thetransmission correcting torque ΔTe (corresponding to the transmissiontorque fluctuation correcting amount Tcv) which can be corrected so asto eliminate the variation of the torque consumed for the transmissionratio changing operation is: ##EQU2## can be obtained, where ωecorresponds to the engine rotation speed.

At step d8, the driving torque Tr is calculated by subtracting thevehicle driving torque correcting amount T_(IV) and the transmissiontorque fluctuation correcting amount Tcv (as the running resistancevalues) from the driving torque Td and is stored in a predeterminedarea. Then, the control process returns to the main routine.

When step a8 is followed by step a9 in FIG. 7, a temporary objectivedriving torque Tvt is calculated by adding the vehicle speed correctiontorque Tv to the driving torque Tr. In addition, at step a10, thetemporary objective driving torque Tvt is divided by the transmissionratio in, and the estimated mechanical loss T_(L) is added thereto tocalculate the objective driving torque Tet. Further, at step a11, theintake air flow (A/N)t corresponding to the objective engine torque Tetis calculated by using a map similar to that illustrated in FIG. 5. Thenthe control passes to step a12.

At step a12, an objective throttle opening Δs is calculated with respectto the intake air flow (A/N)t and the engine speed Ne by using thethrottle valve (accelerator)/intake air flow calculating map illustratedin FIG. 6. The subsequent step a13 calculates a deviation Δ← bycalculating a difference between the objective throttle opening θs andthe actual opening θn to calculate a control amount Phn (i.e. a dutyratio of a pulse signal) with which the deviation Δ← can be eliminated.At step a14, the throttle valve 9 is actuated by supplying the controlamount Phn to the pulse motor 11. In this way, the objective drivingtorque Tvt is generated in the engine.

The CVTECU 21 carries out the CVT control routine illustrated in FIG. 9.Step b1 carries out initialization. Step b2 reads data obtained by thesensors such as the vehicle speed Vc, the throttle valve opening θa andthe actual transmission ratio in to store them in a predetermined area.

At steps b3 and b4, the engine speed Nei corresponding to the objectivetransmission ratio io is calculated based on the actual throttle openingθa by using the map illustrated in FIG. 4. The objective transmissionratio io is determined such that the engine speed Nei is maintaineddepending on an actual vehicle speed Vc. Thereafter, at the step b4, thetransmission ratio deviation Δi between the actual transmission ratio inand the objective transmission ratio io is calculated. Further, thetransmission ratio changing speed Vm corresponding to the value Δi iscalculated so as to be between the minimum and maximum values Vmin andVmax according to the transmission ratio changing speed calculating mapmp1 illustrated in FIG. 13.

At step b5, the primary pressure Pp and the line pressure Prcorresponding to the transmission ratio changing speed are determinedfor the decided transmission ratio changing speed Vm by using a map (seeFIG. 14(b)) (in particular, this embodiment is designed so as tocontinuously apply constant line pressure Pr to the secondary pulley28).

As shown in FIG. 14(a), the effective diameter r1 is considered as beingdirectly proportional to the shift amount Δx (=(1/S)×∫Qdt, where 1/Srepresents a proportional constant) of the pulley in the continuouslyvariable transmission 35. Additionally, the transmission ratio changingspeed Vm (=di/dt) corresponding to the variation of the transmissionratio i is considered as being directly proportional to the variation ofthe effective diameter r1 of the pulley (dr1/dt). Accordingly, thefollowing equation (7) can be derived from the proportional relations,

    d(Δx)/dt=1/(S×Q)=(1/S)×√kΔp (7)

By using this equation (7), the diagram as illustrated in FIG. 14(b) canbe obtained.

In FIG. 14(b), Δp (primary pressure Pp) is considered to represent apressure difference (which is proportional to the fuel flow) in afeeding path of the hydraulic chamber of the pulley. The primarypressure Pp is determined in accordance with the transmission ratiochanging speed Vm (di/dt).

The control process passes to step b6 to set duty ratios Dup and Dur tomaintain the primary and line pressures Pp and Pr. The first and thesecond solenoid valves 33 and 34 are controlled by these duty ratios, sothat the actual transmission ratio in of the continuously variabletransmission 35 approaches to the objective transmission ratio io. Asmentioned above, according to the present invention, it is possible toprecisely control the vehicle speed during the constant speed under thecruise control. Further, it is possible to prevent sudden change of thetransmission ratio. This results in elimination of shock and slip of thesteel belt 27 caused by overpower.

As described above, the present invention basically sets the objectivedriving torque Tet in accordance with the driving torque Td, the vehicledriving torque correcting amount T_(IV), the transmission torquefluctuation correcting amount Tcv, and the vehicle speed correctingtorque Tv. In addition, the output of the internal combustion engine iscontrolled with the objective driving torque Tet. Accordingly, theobjective driving torque Tet can be set by selectively applying thetorque correcting amount depending on the driving conditions. It ispossible to control the internal combustion engine at an optimum powerfor the objective driving torque Tet. Further, it is possible toeliminate slip of the steel belt caused by excessive output and a shockcaused by the transmission operation. Particularly, when the vehicle hasa cruise control device, it is possible to reduce transmission shock ofthe continuously variable transmission during operation of this device,thereby improving driving feelings.

The driving torque Td applied to the vehicle is detected on the basis ofthe intake air flow A/N of the internal combustion engine, and thetransmission ratio i of the continuously variable transmission. Thetransmission torque fluctuation correcting amount Tcv can be controlledin accordance with the transmission ratio changing speed Vm (di/dt) whenthe continuously variable transmission is in the transmission operation.Conversely, Tcv is set to zero when the continuously variabletransmission is not in the transmission operation. Further, theobjective driving torque Tet can be set in accordance with the drivingtorque Td, the vehicle driving torque correcting amount T_(IV) and thevehicle speed correcting torque Tv substantially without using thetransmission torque fluctuation correcting amount Tcv when thecontinuously variable transmission is in the transmission operation. Theaforementioned structure contributes to improving the controllability.

Furthermore, it is possible to change the continuously variabletransmission to a transmission ratio suitable for the driving conditionand to improve the driving feelings when the control device furtherincludes: operational amount detecting means A10 for detecting theoperational amount θa of the driver-operable member for operating theintake air flow adjusting means; objective transmission ratio settingmeans A11 for setting the objective transmission ratio io in accordancewith the operational amount θa; transmission ratio detecting means A12for detecting the actual transmission ratio in of the continuouslyvariable transmission, transmission ratio deviation calculating meansA13 for calculating the deviation Δi between the objective transmissionratio io and the actual transmission ratio in; objective transmissionratio changing speed setting means A14 for setting the objectivetransmission ratio changing speed Vm in accordance with the transmissionratio deviation Δi; and transmission controlling means A15 forcontrolling the continuously variable transmission into the objectivetransmission ratio changing speed Vm.

Industrial Application Field

As mentioned above, in the control device for the internal combustionengine and the continuously variable transmission according to thepresent invention, the continuously variable transmission can be changedat adequate transmission ratio changing speed. In addition, the internalcombustion engine can be controlled at the adequate output inconsideration with output loss caused during transmission ratio changingoperation of the continuously variable transmission. Accordingly, it ispossible to reduce slip caused by the transmission ratio changingoperation and transmission shock caused in the continuously variabletransmission. Further, the present invention is effectively applicableto the driving system where the driving feeling is an important factor.The effect thereof is well exhibited.

We claim:
 1. A control device for controlling an internal combustionengine and a continuously variable transmission of a vehicle, saidcontinuously variable transmission transmitting power between theinternal combustion engine and driving wheels, and having a continuouslychangeable transmission ratio, said control device comprising:drivingtorque detecting means for detecting driving torque applied to thevehicle; transmission ratio changing speed detecting means for detectingtransmission ratio change speed which is a changing rate of thetransmission ratio of said continuously variable transmission;transmission torque fluctuation correcting amount setting means forsetting a transmission torque fluctuation correcting amount as a firstrunning resistance which is consumed for the transmission operation ofsaid continuously variable transmission in accordance with thetransmission ratio changing speed detecting by said transmission ratiochanging speed detecting means; vehicle speed detecting means fordetecting an actual speed of said vehicle; vehicle speed correctingtorque setting means for setting vehicle speed correcting torque, whichis necessary for eliminating a deviation between an objective vehiclespeed for allowing the vehicle to be traveled at a constant speed andthe actual vehicle speed detected by said vehicle speed detecting means,in accordance with said deviation; objective driving torque settingmeans for setting objective driving torque in accordance with thedriving torque detected by said driving torque detecting means, thetransmission torque fluctuation correcting amount set by saidtransmission torque fluctuation correcting amount setting means, and thevehicle speed correcting torque set by said vehicle speed correctingtorque setting means; and output controlling means for controllingoutput of said internal combustion engine in accordance with theobjective driving torque set by said objective driving torque settingmeans.
 2. The control device as claimed in claim 1, wherein saidtransmission torque fluctuation correcting amount setting means sets thetransmission torque fluctuation correcting amount in accordance with thetransmission ratio changing speed detected by said transmission ratiochanging speed detecting means when the continuously variabletransmission is in the transmission operation mode, and sets saidtransmission torque fluctuation correcting amount to zero when saidcontinuously variable transmission is not in the transmission operationmode.
 3. The control device as claimed in claim 1 wherein said drivingtorque detecting means detects the driving torques applied to thevehicle in accordance with an intake air flow of said internalcombustion engine and with the transmission ratio for said continuouslyvariable transmission.
 4. The control device as claimed in claim 1,wherein said output controlling means controls a throttle valve of saidinternal combustion engine in accordance with the objective drivingtorque set by said objective driving torque setting means.
 5. Thecontrol device as claimed in claim 1 further comprising:operationalamount detecting means for detecting an operational amount of adriver-operable member for operating intake air flow adjusting meansdisposed in a suction system of said internal combustion; objectivetransmission ratio setting for setting an objective transmission ratiofor said continuously variable transmission in accordance with theoperational amount detected by said operational amount detecting means;transmission ratio detecting means for detecting an actual transmissionratio of said continuously variable transmission; transmission ratiodeviation calculating means for calculating a deviation between theobjective transmission ratio set by said objective transmission ratiosetting means and the actual transmission ratio detected by saidtransmission ratio detecting means; objective transmission ratiochanging speed setting means for setting objective transmission ratiochanging speed in accordance with the transmission ratio deviationcalculated by said transmission ratio deviation calculating means; andtransmission controlling means for controlling said continuouslyvariable transmission such that an actual transmission ratio changingspeed achieves the objective transmission ratio changing speed set bysaid objective transmission ratio changing speed setting means.
 6. Thecontrol device as claimed in claim 1 further comprising:accelerationdetecting means for detecting actual vehicle acceleration of thevehicle; and driving torque correcting amount setting means for settinga driving torque correcting amount a second running resistance of thevehicle in accordance with the acceleration detected by the accelerationdetecting means.
 7. The control device as claimed in claim 6, whereinsaid objective driving torque setting means sets the objective drivingtorque in accordance with the driving torque detected by said drivingtorque detecting means, the driving torque correcting amount set by saiddriving torque correcting amount setting means, and the vehicle speedcorrecting torque set by said vehicle speed correcting torque settingmeans without using the transmission torque fluctuation correctingamount set by said transmission torque fluctuation correcting amountsetting means when said continuously variable transmission is not in thetransmission operation mode.